1. Field of the Invention
The present invention relates to fuel cell systems.
2. Description of Related Art
In a conventional fuel cell system such as the one disclosed in Japanese Laid-Open Patent Publication No. 2005-158555, an air shut valve and an air pressure control valve are closed to block an air flow to a cathode when initiating or stopping the fuel cell system. Further, hydrogen is supplied from a hydrogen tank to an anode to generate electricity with a fuel cell and to extract power, thereby consuming oxygen remaining at the cathode.
However, in the conventional fuel cell system, cell voltage may become negative in a local cell of the fuel cell on account of a fuel shortage when output current is extracted. In such a state, a catalytic layer which becomes negative thereby may deteriorate